The objective of this project is to elucidate the processes by which the components of T4 bacteriophage become assembled. The process is known to be under the control of many phage genes, mutations in which give rise to a variety of morphogenic defects. The project will now concentrate on the proteolytic cleavage reactions that have been found to accompany T4 assembly. Two small peptide cleavage fragments are found in the phage head which we have previously isolated and characterized. Recently we have shown that one of these fragments can be formed from its protein precursor in vitro by the action of a proteolytic factor present in infected cells but absent from uninfected cells. This in vitro system will be further exploited to positively identify the genes controlling the precursor and the proteolytic factor. The in vitro assay for cleavage will also be used in an attempt to isolate the precursor and the proteolytic factor. If successful, the purified components will then be used to study the biochemical nature and specificity of the cleavage reaction.